Elsevier

The Spine Journal

Volume 14, Issue 3, 1 March 2014, Pages 469-478
The Spine Journal

Basic Science
Aging changes in lumbar discs and vertebrae and their interaction: a 15-year follow-up study

https://doi.org/10.1016/j.spinee.2013.11.018Get rights and content

Abstract

Background context

Many studies have focused on either the intervertebral disc as a culprit in back pain problems, or the vertebral body, but very few studies have examined both structures and their relationship.

Purpose

To measure the concordant changes in morphology of the discs and vertebrae during 5-, 10-, and 15-year follow-ups.

Study design

Longitudinal study.

Patient sample

Among a general population sample of 232 men that had been scanned in 1992–1993, 105 men were reexamined in 1997–1998 and 2007–2008. Mean age at the 15-year follow-up was 63 years. A confirmatory sample with 10 years follow-up was also included.

Methods

Scanners (1.5 Tesla) with surface coils were used at baseline and follow-up. Image analyzing software was used to measure distances and areas of interest of midsagittal and midaxial spine images.

Results

The disc heights decreased at 5 years by 3.4% (0.4 mm) and 3.3% (0.4 mm) and at 15 years by 8.7% (1.0 mm) and 11.3% (1.3 mm) in the upper and lower discs, respectively (p<.001). Although not clear after 5 years, vertebra heights increased in mean by 3.1% (0.8 mm) in the upper lumbar levels and by 4.7% (1.1 mm) in the lower vertebrae after 15 years (p<.001). Vertebra height increases were associated with disc narrowing (p=.001). The mean annual shortening of the lumbar spine L1–S1 block was 0.13 mm/y, which was in line with the mean standing height that decreased little (174.7 cm at baseline and 174.4 cm at the follow-up).

Conclusions

Discs and vertebrae degenerate or remodel in concert: decreases in disc height appear to be compensated, in part, by accompanying increases in adjacent vertebra heights. The mechanism behind this novel finding and its implications require further study.

Introduction

Many studies have focused on either the intervertebral disc, as it is believed by many to be a culprit in back pain problems, or the vertebral body, typically related to osteoporotic fracture or Modic changes, but very few studies have examined both the structures and their relation. Several investigations of lumbar vertebral bone mineral density (BMD) in relation to disc degeneration have been conducted, with most suggesting that higher vertebral BMD is associated with more disc degeneration [1], [2], [3]. Analyses of autopsy material, using estimates of disc degeneration from discography and vertebral BMD from microcomputed tomography, showed more specifically that higher BMD of the vertebral body and greater end plate thickness were associated with more disc degeneration [4]. Based on another study of 27 cadavers, Simpson et al. [5] hypothesized that disc “disorganization significantly modulates bone degeneration that could influence the incidence of vertebral body crush fracture.” Moore at al [6] found in a study of sheep that “outer anular injury” was associated with greater vertebral trabecular bone volume. Overall, these studies suggest an interaction between the degeneration or pathogenesis of discs and vertebrae, but longitudinal studies are needed to clarify these relations and others. A number of investigators have conducted longitudinal studies of disc herniations after surgery, “Modic changes” [7], [8], or qualitatively assessed disc degeneration [9]. Yet, we are aware of no longitudinal studies that investigate the concurrent changes in morphology of the discs and vertebrae and their interaction.

Better understanding of pathogenesis has commonly enhanced prevention and led to more rational treatment of underlying illnesses. Our goals were to describe the changes in shape and size of lumbar vertebrae and discs occurring over a 15-year period in a general population sample of men using quantitative magnetic resonance imaging (MRI) measures and visual assessments.

Section snippets

Subjects

Participants for this study were selected from the 232 monozygotic (MZ) twins initially recruited in the Twin Spine Study, which were drawn from the population-based Finnish twin cohort that included all same-sex twins born in Finland before 1958 and still alive in 1975 [10]. The initial selection of MZ twins, which has been described in detail previously [10], was based on co-twin discordance for one of the common environmental exposures, primarily occupational or leisure physical activities.

Vertebra changes based on quantitative measures

After 5 years, the vertebra height and width increases (0.4% and 0.4% mean increases in the upper lumbar discs and 0.2% and 0.1% in the lower discs, respectively) were not statistically significant (Table 1). Over 15 years, however, the vertebra heights increased in mean by 3.1% (0.8 mm) in the upper lumbar levels and by 4.7% (1.1 mm) in the lower lumbar levels (p<.001, respectively). The largest increases in mean upper and lower vertebra heights were 8.6% (2.0 mm) and 16.8% (3.5 mm; Fig. 2,

Discussion

Lumbar disc height decreased over a 15-year period by approximately 9% to 10% on an average in the upper lumbar region and 12% to 13% in the lower lumbar discs in our population-based sample of middle-aged men, but the variations observed among individuals were large. Some had no apparent progression of disc degeneration, whereas others had dramatic disc height loss. The surprising finding, however, was a mean increase in the lumbar vertebra height that was associated with adjacent disc height

Conclusion

While discs and vertebrae appear to change in concert, the finding of increased vertebra height awaits replication.

Acknowledgments

Supported by the NIH NIAMS; The Work Environment Fund, Finland; The Alberta Heritage Foundation for Medical Research, Canada; and the Canada Research Chairs Program.

The authors thank Dr. JDG Troup for his helpful comments and suggestions.

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FDA device/drug status: Not applicable.

Author disclosures: TV: Nothing to disclose. MCB: Nothing to disclose. LEG: Consulting fee or honorarium: University of Alberta (A) KG: Nothing to disclose.

The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.

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